Re: [matplotlib-devel] release strategy and the color revolution

[Michael W. <mw...@st...>]

Hey Olga,

On Tue, Feb 17, 2015 at 6:24 PM, Olga Botvinnik <obo...@uc...> wrote:

> Out of curiosity, what are the advantages of the HCL colormap over YlGnBu
> for continuous values? I'm biased towards YlGnBu because green is my
> favorite color and want to know what makes HCL objectively better for
> perceiving values.
>

Perceptually, the luminance ramp is probably a bit more linear, but that's
not a huge deal. The main functional advantage to using *some* kind of Hcl
based map is that it lets matplotlib tweak more parameters. This particular
Hcl map has a bit more hue variation than YlBuGn, and I think the
saturation channel is doing something different than what the colorbrewer
maps do. So it appears a little bit more "colorful", which I think was one
of the objectives.

I think there's some argument for matplotlib creating a novel colormap for
its default rather than just using one of the preset colorbrewer ones. It
would be nice to have a bit more well-defined visual identity, and having
people say "oh hey that's the matplotlib colormap, it looks really nice!"
might have good marketing benefits. I like the colorbrewer palettes and use
them often, but it seems kind of boring to take an existing colormap that
lots of packages have and make it the default.


> I added YlGnBu_r versions of those plots just below yours:
> http://nbviewer.ipython.org/gist/olgabot/6a619ef21c178801ff77
>
> It seems it's a little more "extreme" than HCL, as in it lights are
> lighter and its darks are darker. From the color research, is this less
> desirable?
>

Well, that could be changed in the Hcl version by setting different
endpoints for the lightness ramp. I was trying to get something similar to
parula, which doesn't cover as extreme of a lightness range and is more
saturated on both ends than the color brewer palettes. I would imagine the
reasoning for this is that it might let the map represent categorical or
divergent data a little bit better without much cost to sequential data,
but I am not sure.

Also, if you map a line or scatter plot with YlGnBu, the lightest colors
might not be visible on a white background, whereas I think the yellow I
used would be ok. This might be something to keep in mind as the map that
gets chosen will likely be the default for plt.scatter.

But like I said, I didn't spend much time thinking about exactly where the
endpoints should be, so it's possible one would want more dynamic luminance
range.

Michael


> On Mon Feb 16 2015 at 9:28:56 PM Benjamin Root <ben...@ou...> wrote:
>
>> Do remember that I have a PR to add linestyle cycling, which would
>> greatly mitigate problems for colorblindness and non-color publications.
>>
>> I also prefer it for slideshows as projectors at conferences tend to have
>> crappy colors anyway (was at a radar conference when the projector's red
>> crapped out while the presenter was building up suspense about the really,
>> really impressive radar image of a supercell on the next slide)
>>
>> Ben Root
>> On Feb 16, 2015 7:24 PM, "Michael Waskom" <mw...@st...> wrote:
>>
>>> See [here](http://nbviewer.ipython.org/gist/mwaskom/6a43a3b94eca4a9e2e8b)
>>> for a quick and dirty implementation that should get a general idea. This
>>> probably ins't the best way to do it -- anyone should feel free to build on
>>> this.
>>>
>>> On Mon, Feb 16, 2015 at 3:38 PM, Eric Firing <ef...@ha...> wrote:
>>>
>>>> On 2015/02/16 1:29 PM, Michael Waskom wrote:
>>>>
>>>>  Nathaniel's January 9 message in that thread (can't figure out how to
>>>>> link to it in the archives) had a suggestion that I thought was very
>>>>> promising, to do something similar to Parula but rotate around the hue
>>>>> circle the other direction so that the hues would go blue - purple -
>>>>> red
>>>>> - yellow. I don't think we've seen an example of exactly what it would
>>>>> look like, but I reckon it would be similar to the middle colormap here
>>>>> http://earthobservatory.nasa.gov/blogs/elegantfigures/
>>>>> files/2013/08/three_perceptual_palettes_618.png
>>>>> (from the elegant figures block series linked above), which I've always
>>>>> found quite attractive.
>>>>>
>>>>
>>>> Certainly it can be considered--but we have to have a real
>>>> implementation.
>>>>
>>>>
>>>
>>>
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